MR 3.3 Comment 10 -- Remedial Measures

[10] Having offered material evidence in the belief that it was true, a lawyer may subsequently come to know that the evidence is false.
Or, a lawyer may be surprised when the lawyer's client, or another witness called by the lawyer, offers testimony the lawyer knows to be false, either during the lawyer's direct examination or in response to cross-examination by the opposing lawyer.
In such situations
or if the lawyer knows of the falsity of testimony elicited from the client during a deposition,
the lawyer must take reasonable remedial measures.
-- In such situations, the advocate's proper course is to
--- remonstrate with the client confidentially,
------advise the client of the lawyer's duty of candor to the tribunal
----- and seek the client's cooperation with respect to the withdrawal or correction of the false statements or evidence.
If that fails, the advocate must take further remedial action.
--If withdrawal from the representation is not permitted
---- or will not undo the effect of the false evidence,
--the advocate must make such disclosure to the tribunal as is reasonably necessary to remedy the situation,
---- even if doing so requires the lawyer to reveal information that otherwise would be protected by Rule 1.6.
It is for the tribunal then to determine what should be done -- making a statement about the matter to the trier of fact, ordering a mistrial or perhaps nothing.